On PHPMaster.com today there's a new article emphasizing something that lots of developers forget to make a part of their process when writing code - creating useful documentation to help make your code that much clearer.
If you're writing code that will be shared with others, put yourself in their shoes. Don't let your project lose potential users, community members, and possible contributors all because of insufficient documentation.
He (Matthew Turland) suggests a few things to keep in mind as you're writing up your documentation - the content is "king" (an emphasis on good descriptions/examples/use cases), open it up to external contributions using things like wikis (or even stored in the source code repository) and a focus on technical writing skills. Even the best tools out there can suffer if there's poor or no documentation.